The invention relates to a device for monitoring the combustion processes occurring in the combustion chamber of an internal combustion engine.
The development of internal combustion engines —both spark ignition and diesel engines —requires the widest possible knowledge of the processes occurring during combustion in order to reduce further both the fuel consumption and the emissions of exhaust gases and noise.
In order to be able to observe and analyze the combustion process —and phenomena associated with it—various optical measuring methods and measuring devices have been developed in the last few years. In the predevelopment and series development of internal combustion engines, it is, however, possible —in contrast to the basic research —to apply only methods and devices in which the necessary optical accesses to the combustion chamber are configured in such a way that the shape of the combustion chamber and, for example the thermal state of the combustion chamber walls, remain largely unchanged.
With these known methods and devices, the light that is emitted by the flame in the combustion space is extracted from the combustion space by means of lightguides and fed to a light/voltage transducer (photomultiplier, photodiode or CCD array). The electrical voltage present in these transducers is proportional to the intensity of the light and can be converted by means of A/D converters into digital data which can be electronically processed. Therefore, these methods and devices do not require any electrical auxiliary voltages or supply voltages or injection of extraneous light (for example by means of laser light).
DE-A1 198 30 213 discloses a device for monitoring the combustion processes occurring in the combustion chamber of an internal combustion engine, in the for, of a spark plug for internal combustion engines, in which spark plug a group of lightguides is installed at the circumference of the housing of the spark plug in order to be able to analyze the flash phase after the actual ignition and the early propagation phase of the flame. With this device, it is possible to see into only part of the combustion chamber, and observation oz the propagation of the flame with local resolution in the combustion chambers of engines is possible, even then only to a restricted degree, if a plurality of collection drilled holes provided in the spark plug are connected to one another by an each case a few lightguides of the group.
The same also applies to a device disclosed in DE-A1-198 23 594 in which a lightguide is provided which is integrated into a cylinder head seal and brings about a connection between the combustion chamber and an evaluation unit. The lightguide opens here into the combustion chamber via a translucent sealing element.